1. Technical Field
The invention relates to an ultra wide-angle imaging lens device and an imaging apparatus, particularly, to an ultra wide-angle imaging lens device that is suitable for use in an on-vehicle camera, an onboard camera, a cell phone camera, a surveillance camera, or the like having an imaging device such as a CCD (Charge Coupled Device) sensor or a CMOS (Complementary Metal Oxide Semiconductor) sensor, and to an imaging apparatus having the ultra wide-angle imaging lens device.
2. Description of the Related Art
In recent years, an imaging device such as a CCD sensor and a CMOS sensor has been more downsized and increased in the number of pixels. Accordingly, an imaging apparatus main body having such an imaging device has been also downsized, and a lens mounted thereon is required to be reduced in size and weight.
Also, an imaging lens device used in an on-vehicle camera, a cell phone camera, a surveillance camera, or the like is required to have high image quality in the overall effective picture plane even with its wide angle of view, in order to secure a good visual field in a wide area.
JP 2002-244031 A, JP 2006-259704 A (corresponding to US 2006/0187557 A), JP 2006-292988 A (corresponding to US 2006/0227434 A), and JP 2005-227426 A describe wide angle imaging lens devices having a relatively small number of lenses in the field mentioned above. JP 2002-244031 A, JP 2006-259704 A and JP 2006-292988 A describe wide angle lenses which have a four-lens configuration. JP 2005-227426 A describes a fisheye lens which has a four-lens or five-lens configuration.
However, in the lens described in JP 2002-244031 A, a refractive index of the first lens located on the most-object side is low, and negative powers of the first and second lenses are relatively low. Hence, it is hard to obtain an angle of view greater than 180 degrees, and recent demand of an increase in angle of view can not be satisfied. In the lens described in JP 2006-259704 A and JP 2006-292988 A, angle of views of them are in the range of 140 to 165 degrees and around 160 degrees, respectively, and recent demand of an increase in angle of view can not be satisfied.
In the lens described in JP 2005-227426 A, although its angle of view is greater than 180 degrees, there is a room for improvement in optical performance. In this lens, when the lens is estimated based on a stereographic projection, distortion rapidly increases toward a negative side in the area where a half angle of view is greater than 80 degrees. Thus, an image in the most peripheral portion is shrunken and is formed as a small image.